1. Field of the Invention
This invention relates to methods and apparata used in cannulation techniques, and particularly, to an improved cannula apparatus and method for its insertion suitable for use in a cardiac cannulation technique.
2. Description of the Prior Art
A cannula, or catheter as it may be called, is generally recognized as an elongated and flexible tube that may be inserted into a person's body in order to withdraw or inject various fluids. The prior art is replete with such cannulas and catheters, as well as with methods for their insertion and use.
The use of inflatable balloons with such cannulas and catheters is also known in the art. In one instance, commonly referred to as a "bag" catheter, an externally-attached balloon or "bag" is used to hold the catheter in place after insertion in order to allow prolonged or periodic withdrawal or injection of fluids into the body. A common use for such "bag" catheters, as disclosed in Rocchi et al., U.S. Pat. No. 3,331,371, is to insert the catheter by way of the urethra into a person's bladder in order to withdraw fluid from the bladder over a protracted period of time. Another example of an externally-attached inflatable balloon or collar used to stabilize the position of the cannula following insertion is found in Shinnick et al., U.S. Pat. No. 3,680,544, which discloses a transthoracic cannula-type device useful in cardiopulmonary resuscitation.
In other instances, inflatable balloons have been positioned inside the luminal cavity in the cannula or catheter in order to achieve a desired result. In Kim, U.S. Pat. No. 2,919,697, such an intraluminal inflatable balloon was used for the same purpose as above described, i.e., for anchoring the standard catheter drainage tube in the body after insertion. The above Rocchi reference, on the other hand, uses the intraluminal balloon or ball to completely cover the fluid entrance holes in the catheter and thereby control the flow of fluid therethrough.
A rapidly-growing area of cannula technology concerns the technique of cardiac cannulation and the use of artificial heart-lung machines to facilitate intricate and prolonged operations on the cardiac, pulmonary and circulatory systems. During such operations, cannulas which are connected to the artificial heart-lung machine are first properly inserted through prepared incisions into the arterial and venous systems adjacent the heart, and even into the intracardiac chambers as well. Once properly positioned and in operation, the blood of the person is withdrawn or siphoned through the venous cannulas and pumped through the arterial cannulas back into the circulatory system by the artificial heart-lung machine. The heart and lungs of the person can thereby be effectively bypassed, thus allowing the surgeon to operate on the heart.
A major problem encountered in all such cardiac cannulation techniques involves the introduction of air into the circulatory system during the insertion and positioning of the various venous, arterial and intracardiac cannulas. In this regard, the avoidance of any such introduction is extremely important because of the danger of stroke or other adverse effects such air may have on the circulatory system.
The present state of the art provides two possible methods for avoiding any such introduction of air during cardiac cannulation. One method involves first inserting the distal end of the cannula into the circulatory system while the tubing connecting the cannula to the heart-lung machine is clamped shut by external means. The entrapped air is then vented by manipulating a drain line near the proximal end of the cannula thereby permitting the cannula to fill with the patient's blood. This method, however, does not prevent the possible introduction of air into the blood stream during initial insertion of the distal end of the cannula. In addition, it requires the extra steps of manipulating both the venting line and the external clamp, and cannot prevent the probable entrapment of air in the tube between this venting line and the clamp itself.
A second method of cannula insertion practiced in the present art involves first holding the cannula upright and filling it either with a serum or with blood through the plurality of holes near its closed distal tip. Then, the surgeon rapidly inserts the distal end of the cannula into the prepared incision in the circulatory system in order to avoid excessive spillage of the fluid, if at all possible. This method has its shortcomings both because of the mess created by the spilling fluid and because as the fluid empties, air may be again allowed into the cannula and later introduced into the circulatory system.